Double antiferromagnetism in Heusler-type alloys Fe2+xV1-xSi

Measurements of transport and magnetic properties, 57Fe-Moessbauer spectroscopy and 51V-NMR were performed for a Heusler-type alloy series Fe2+xV1-xSi (0.00 ≤ x ≤ 0.08). In Fe2 VSi (x=0.00), which had been reported to be an antiferromagnetic metal with the Neel temperature TN1=123 K, another antiferromagnetic transition was found at 34 K (TN2). The Neel temperature TN1 was found for the alloys with x less than 0.08: it decreased monotonically with increasing x. The new antiferromagnetic transition temperature TN2 was also found for x=0.02 at 64 K. The characteristic hysteresis observed in the magnetization curve below TN2 was macroscopic evidence for the occurrence of another antiferromagnetic ordering. The presence of two types of magnetic transition at ∼40 and ∼120 K for Fe2 VSi was confirmed microscopically by Moessbauer spectroscopy. The Moessbauer and NMR measurements showed the presence of slight Fe/V antisite disorder, which plays an important part in the magnetic order below TN2. The magnetic structure of Fe2 VSi was discussed and the idea of double antiferromagnetism was proposed. (author)